1. Field of the Invention
The present invention relates to a novel GMP synthetase and a DNA that codes for it. A microorganism that has GMP synthetase and its enzymatic activity can be used for the production of nucleic acid compounds such as guanosine 5'-monophosphate, which is useful as a raw material of seasonings and so forth.
2. Description of the Related Art
In the conventional production of nucleic acid compounds such as guanosine 51-monophosphate (also called 5'-guanylic acid, hereinafter abbreviated as "GMP") and guanosine by fermentation, mutant strains that are imparted with adenine auxotrophy and nucleic acid analogue resistance have been utilized in a medium containing a limited amount of adenine compounds (Japanese Patent Publication (Kokoku) Nos. 55-2956/1980 and 55-45199/1980).
Usual mutagenesis treatments often introduce mutations in genes of resulting mutant strains other than a target gene. In addition, because complicated controlling mechanisms are present in the biosynthetic pathways of nucleic acid compounds, it is difficult to obtain a microorganism that produces a marked amount of a certain nucleic acid compound. Therefore, mutant strains obtained by conventional methods for breeding bacterial strains have not necessarily been satisfactory strains.
GMP is synthesized by an amination reaction catalyzed by GMP synthetase and utilizing L-glutamine as an amino group donor from 5'-inosinic acid (IMP) via xanthylic acid (XMP). Therefore, there has been proposed a method for producing GMP which utilizes Escherichia coli transformed with a GMP synthetase gene (guaA) of Escherichia coli (Japanese Patent Publication (Kokoku) No. 7-16431/1995). The guaA gene has been isolated from Bacillus subtilis (J. Bacteriol., 174, 1883-1890 (1992), EMBL/GenBank/DDBJ Accession M83691), Corynebacterium ammoniagenes (Korean Patent Publication No. 96-7743, EMBL/GenBank/DDBJ Accession Y10499), Borrelia burgdorferi (J. Bacteriol., 176, 6427-6432 (1994), EMBL/GenBank/DDBJ Accession L25883), Dictyostelium discoideum (J. Biol. Chem., 266, 16448-16452 (1991), EMBL/GenBank/DDBJ Accession M64282) and so forth.
However, no guaA gene of Brevibacterium lactofermentum (Corynebacterium glutamicum) has been known.